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Astron. Astrophys. 326, 842-850 (1997)

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Granulation and magnetism in the solar atmosphere *

F. Baudin 1, R. Molowny-Horas 1 and S. Koutchmy 2

1 Instituto de Astrofsica de Canarias, E-38200 La Laguna, Tenerife, Spain
2 Institut d'Astrophysique de Paris, CNRS, 98bis Bd Arago, F-75014 Paris, France

Received 28 May 1996 / Accepted 20 May 1997

Abstract

The properties of the photosphere in magnetic and non magnetic regions, at two levels in the solar atmosphere, have been studied, using two virtually simultaneous time sequences of 109 mn duration of CCD images taken at the Vacuum Tower Telescope of the Sacramento Peak Observatory. The selected wavelengths correspond to the true continuum and to the wing of the MgIb1 line, where brightenings are taken as proxies of magnetic elements. Averaged intensities, intensity fluctuations and horizontal motions in different regions and levels of the photosphere have been compared. We obtained various results concerning: the intensities inside and outside an active region showing different behaviours; the granulation keeping a kind of remnant structure at the continuum level; the mapping of proper motions of the granules imaged in the continuum outlining clearly the super-granular cells in the deepest layers of the photosphere; the "freezing" influence of the magnetic field on these motions in active regions; and the temporal variation of the correlation between images at the two heights indicating that intensity variations at the higher level precede those of the lower one.

These results are briefly discussed and compared with previous ones and with published model calculations.

Key words: Sun: photosphere; granulation; magnetic fields; activity - convection

* Based on oberservations made at the Vacuum Tower Telescope of the National Solar Observatory/Sacramento Peak Observatory (New Mexico, USA)

Send offprint requests to: S. Koutchmy

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© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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